What Kind of Rock Is This?
ES0610  Marble Reaction with Hydrochloric Acid

Drop a small amount of dilute hydrochloric acid on an area of your sample that has been scratched by a nail.

  !   Click each image to see positive and negative results of the acid test.

Matthew Nyman, TERC
Powdered marble reacts with hydrochloric acid to release bubbles of carbon dioxide gas. If the acid fizzes on your sample, your rock is probably marble. Wipe all acid off the rock sample with a paper towel.
Matthew Nyman, TERC
If the acid only makes the rock wet, wipe the rock with a paper towel, and go back to homogeneous-looking rocks.

If you have identified your sample, return to the beginning of the rock identification key, select another rock sample, and begin the process over again.

If your rock sample does not have any of the features described on this page, reexamine the rock with a hand lens or magnifying glass. Look at the sample from all angles. Concentrate on fresh surfaces where you might be able to better determine the texture. Return to the beginning of the rock identification key and start over again.